Lessons Microsoft can teach us that we still haven't learned: Platforms are important.
The problem with getting rid of applets isn't so much that applets are so useful as it is that stuff that worked in GNOME 2.x will just stop working in 3.x. Microsoft's 'platform' may be a maze of half-broken crap and shims for legacy support, but on the other hand everything that actually worked tends to stay working. So applets don't support some awesome GNOME Shell vision? So what! Grandfather them in, mark them as deprecated and move on. If it turns out that the new way really is superior people will port (in their own good time) and meanwhile everything compiles and users can still get to the functionality to which they have grown accustomed.
When a third party program that used to work in an old release doesn't work in a new release I call it a regression and I blame GNOME, not the third party.